This invention relates to an optical micro-machining method of glass by utilizing selective etching due to irradiation of light.
It is known that when a strong ultraviolet ray is applied to oxide glass, particularly SiO.sub.2 type glass, its density and refractive index become higher. It is also known that a similar phenomenon occurs on the surface of glass into which various ions such as transition metal ions are implanted. Generally, the area in which such a high density occurs has lower chemical durability than other areas. Therefore, when etching is carried out by an aqueous hydrofluoric acid solution, selective etching takes place in the light irradiated area. However, because the etching rate of light radiated glass is only about three times that of unprocessed glass, this rate is not yet sufficient for forming a diffraction grating or an optical waveguide on the glass surface or forming a fine pattern of an inorganic resist film on a semiconductor substrate.